Investigations on the color of central elliptical galaxies of the cooling core clusters for the possible signature of AGN-ICM feedback.
Cluster of galaxies:
Cluster of galaxies are the largest gravitationally bound structures in the Universe. The study of the phenomena happening in clusters sheds much light into the understanding of the evolution of the structures in the universe. It is observed that the cluster of galaxies mostly have a central big elliptical galaxy. According to theory, a flow of intra cluster gas towards the central galaxy is expected and is termed as the cooling flow.
Origin of cooling flows and the cooling flow problem:
This should happen as the ICM (Intra Cluster Gas) in the plasma form is quickly losing its energy by the emission of X-rays. The X-ray brightness of the ICM is proportional to the square of its density, which rises steeply towards the centre of many clusters. Also the temperature falls to typically a third or a half of the temperature in the outskirts of the cluster. As material in the centre of the cluster cools out, the pressure of the overlying ICM should cause more material to flow inwards (the cooling flow). It is currently thought that the amount of cooling are in reality much smaller than expected, as there is little observational evidence for cool X-ray emitting gas in many of these systems. This is the cooling flow problem.
The AGN feedback - a plausible solution to the cooling flow problem?
Cooling flow galaxies frequently host strong central radio sources. Some also show a weaker radio halo, which may be caused by relativistic particles accelerated by the compression of magnetic field lines trapped in the collapsing gas. It is observed that 71% of cD galaxies located in cooling flows are radio-loud.
Heating by central AGN (Active Galactic Nuclei) feedback of these galaxies is the most popular solution for the cooling flow problem. The AGN_ICM feedback through radio emissions (radio mode feedback), which is capable of blowing radio bubbles into the hot ambient gas displacing it, have been recently adjudged as one of the possible reasons for the heating of the cluster medium. This feedback is expected to substantially affect the cooling flow.
Enhancement of Star Formation Rate (SFR)- a signature of the cooling flow:
It is expected that due to the flow of gas from the outskirts of the clusters, the star formation Rate at the central galaxies will get a boost. So, Star Formation rate at the central galaxies can be taken as a measure of the cooling flow. The star formation rate can be estimated, through various empirical relations, from the colors of the photometric images of the galaxies in various bands. If the cooling flow is getting disrupted due to the AGN heating mechanism, we expect a difference in the star formation rate in the central cD galaxies with radio feedback and without that.
The proposed project is to estimate the colors of samples of central cD galaxies with and without AGN feedback and to compare the estimated SFR and to connect the observation to the cooling flows.
The colors of the photometric images or the galaxies will be estimated using IRAF (Image Reduction and Analysis Facility) software which runs on Linux Operating System. During the course of the workshop, the student will be familiarized with the package and the method for finding the color.
The sample of images can be downloaded from the Sloan digital Sky Survey (SDSS) catalogue, which is available online, using simple SQL Queries.
A basic knowledge of cluster of galaxies, central elliptical galaxies of clusters, radio emissions from AGN, colour of galaxies and its importance in photometric studies and working knowledge of IRAF (desirable),.
Key words for search: cluster of galaxies, cooling flows, Star Formation Rate, Color in galaxies, AGN_ICM feedback